In recent ten years, due to the discharge of domestic sewage, the water quality of Jiuqu River in Ziyang is seriously eutrophic, and the water body turns green and stinks from time to time, which is harmful to fisheries and residents' health. (1) Cyanobacteria are autotrophs and producers in the ecosystem, and they are in the first trophic level. As can be seen from the table, the feeding habit of chain fish is phytoplankton, so the most suitable fish for release is silver carp.

(2) From the perspective of biological control, other aquatic organisms with economic value should be released in the middle and lower reaches of the Yellow River to increase species and improve the self-regulation ability of the ecosystem.

(3) According to the gradual decrease of energy flow in the ecosystem, it can be concluded that B, D, A and C are in the first, second, third and fourth trophic levels respectively, and then according to the energy transfer efficiency = energy assimilated by the next trophic level/energy assimilated by the next trophic level, the energy transfer efficiency from the second trophic level to the third trophic level = 15.9/65438+.

(4) People along the coast also discharged some environmental hormone chemicals into Jiuqu River in their production and life. These substances can be introduced into the human body along the food chain, and will interfere with the normal metabolism of cells after being accepted by the receptors on the target cell membrane, thus destroying the steady state of the human body. The main regulatory mechanism of maintaining the homeostasis of human internal environment is nerve-humoral-immune regulatory network.

So the answer is:

(1) first trophic level

(2) Improve the stability of ecosystem resistance (or enhance the self-regulation ability of ecosystem)

(3) 1 1.3%

(4) food chain? Receptor protein (or glycoprotein)? Neural-humoral-immunoregulatory network